The 10w 40 is not Diesel rated (CJ etc) Go with the Motorcraft. But if they were both diesel rated the 10w 40 would actually be better. It will flow better for starts and cooler weather yet still have the same film viscosity when up to temp. It will ave a bit more VI additive which is what shears but its very minimal.
A forum community dedicated to Ford Power Stroke owners and enthusiasts. Come join the discussion about diesel performance, modifications, EGR deletes, troubleshooting, lift kits, tires, wheels, maintenance, and more!